The data of a volume that is managed by the storage system has been backed up conventionally. As the backup, a method for managing a snapshot in a state of a volume at a predetermined point of time has been known for instance.
In the case in which a snapshot is managed, when a write access occurs for a volume of a save source (a primary volume), the data of a region of a write destination of a primary volume is saved to a volume of a save destination (a secondary volume). After that, the data of a write target is copied to the primary volume, and a response is returned to a write access source. Consequently, it takes a long period of time to return a response to the write access source from an occurrence of the write access occurs, whereby a write response is deteriorated unfortunately.
On the other hand, the copy after write (CAW) technique has been known (see Patent Literature 1 for instance). For the copy after write (CAW) technique, in an occurrence of the write access, the write data is stored to a cache memory, a response is returned to the write access source, the data of a primary volume is saved to a secondary volume in an asynchronous manner with the write access, and the write data of the cache memory is written to the primary volume, whereby a write response is speeded up.